Combined Effect of Degassing and Recycling on Mechanical Performance of Cast EN AC-43200 Aluminum–Silicon Alloy

The manuscript investigates the effect of degassing on the mechanical performance of recycled EN AC-43200 (AlSi10Mg(Cu)) alloy produced by permanent-mold gravity casting. Quasistatic tensile and high cycle fatigue measurements are performed on specimens with different porosity levels (0.02% ≤ %Pvol ≤ 1.3%) obtained by modifying the degassing process time. Detailed x-ray tomographic investigation and surface fracture analysis demonstrate that: (a) quasistatic properties show a linear trend with the porosity degree and as the %Pvol decreases from 1.1 ± 0.2 to 0.02 ± 0.01%, the UTS, Rp0.2, and E increase from 261 ± 10 to 276 ± 4 MPa, from 304 ± 3 to 319 ± 5 MPa, and from 72.2 ± 0.4 to 76 ± 0.8 GPa, respectively; (b) at high porosity concentration (e.g., %Pvol ≥ 0.5%) gas pores clearly affect both fatigue initiation and propagation; (c) when %Pvol is lower than 0.06%, the effect of casting defects, such as micro-shrinkage pores and entrapped oxides, competes with gas pores in initiating the fatigue crack. Additionally, careful SEM-EDXS analyses reveal that brittle Fe/Mn-rich intermetallic precipitates are typically present alongside both gas and micro-shrinkage pores, further amplifying their role as stress risers. These results emphasize the complex relationship between the casting process, microstructure, and the mechanical performance of recycled AlSi alloys, providing valuable insights for the future design of components with a low carbon footprint.